This invention relates to hydraulic actuation systems and in particular hydraulic actuation systems for automated transmission systems.
In automated transmission systems of, for example, the type disclosed in WO97/05410; WO97/40300: GB0005186.2; GB0024999.5 or GB0025000.1, whose content is expressly incorporated in the disclosure content of the present application, fluid pressure actuators are used to control actuation of a clutch actuator mechanism and/or a gear engaging mechanism.
In such systems solenoid control valves are used to control flow of fluid to and from the fluid pressure actuators, so as to control actuation of the clutch and the gear engagement mechanism.
With increasing sophistication of such systems, three or four proportional flow control valves are typically used to control the system. These control valves are normally spool valves having multiple lands and ports. Moreover the valves must be controlled typically to move between three or four positions. These valves are as a consequence relatively expensive and require complex electronic control systems, which adds considerably to the overall cost of the hydraulic actuation system.
The present invention provides a simplified hydraulic actuation system with a view to reducing the cost and complexity of the system.
According to one aspect of the present a hydraulic actuation system for an automated transmission system comprises:
a source of hydraulic fluid under pressure;
a hydraulic fluid reservoir;
a hydraulic clutch actuator for controlling engagement of a clutch, said hydraulic clutch actuator comprising a single acting ram with a single working chamber;
a hydraulic gear engagement actuator for controlling engagement of a gear, said hydraulic gear engagement actuator comprising a double acting ram comprising first and second working chambers;
a main control valve, the main control valve being switchable between a first position in which the clutch actuator and gear engagement actuator are connected to the source of fluid under pressure and a second position in which the clutch actuator and gear engagement actuator are connected to the reservoir;
the working chamber of the clutch actuator being connected to the main control valve via a clutch control valve, the clutch control valve being switchable between a open position in which the working chamber of the clutch actuator is connected to the main control valve and a closed position in which the working chamber of the clutch actuator is isolated from the main control valve;
the first and second working chambers of the gear engagement actuator being selectively connected to the main control valve or to the reservoir via first and second gear control valves respectively.
The hydraulic actuating system described above replaces the complex proportional flow control valves used hitherto with simple two position solenoid control valves. Even though this entails the use of more valves, this will nethertheless reduce to overall cost of the system and significantly simplify the electronic control system required to control the valves. The main control valve permits the system to be depressurised and reduces the number of potential leakage points, when the system is not in use.
According to a preferred embodiment of the invention a pair of gear engagement actuators are used, a select actuator to control movement of a selector mechanism in a first xe2x80x9cselectxe2x80x9d direction and a shift actuator to control movement of the selector mechanism in a second xe2x80x9cshiftxe2x80x9d direction. Each of the select and shift actuators are provided with first and second gear control valves.